devel/gprbuild: Upgrade version 20150506 => 20160609
GPRBuild build is now hosted on github, so we can move away from the
yearly releases and update more frequently. Unfortunately the docs
makefile is currently broken so docs are disabled currently. When
they come back, only txt and html docs will be supported.
This new version detected a missing reference in the template-parser
port so that port has been fixed and the downstream ports bumped
accordingly.
It also discovered an interface specification issue in a designer
example of qtada. I spent a few minutes trying to fix/workaround it,
but ultimately marked it broken. I will also deprecate the port because
it no development has occurred since the port was created, and it's not
even based on a real release. We'll see if anybody cares (3 month
deprecation).

Change Ada Framework foundation from gcc5-aux to gcc6-aux
GCC 6.1 was released this week. The Ada Framework in FreeBSD ports has
been based on GCC 5.3 GNAT although GCC 6.x has been supported for awhile
via the ADA_DEFAULT option in make.conf.
Now that GCC 6 has been officially released, switch to it by default.
People can maintain the old foundation by putting "ADA_DEFAULT=5" in
/etc/make.conf.
Libraries built by one GNAT are unusable by another, so almost every Ada
port has been bumped as a result. Noticable exceptions are dns/ironsides
which fails to build on gcc6 (thus USES=ada:5 is set) and cad/ghdl which
needs additional testing as it may require gcc5 on FreeBSD (DragonFly
uses the LLVM backend only).

Tie libgnat_util.a to libasis
Rather than specify gnat_util every time ASIS is a dependency, set it
as a library dependency for ASIS. LIB_DEPENDS doesn't work because it
is a static library, so just manually add libgnat_util.a to BUILD_DEPENDS
and RUN_DEPENDS, then adjust 3 ports accordingly.